Key areas Nuclear equations to describe radioactive decay, fission and fusion reactions with reference to mass and energy equivalence including calculations.

What we will do today: Explain what is meant by alpha, beta and gamma decay of ‘radionuclides’. Describe the process of radioactive decay in ‘symbol form’.

Nuclear Reactions

Structure and Symbols. Atomic Number – The number of protons in the nucleus (Z) – also equal to the number of orbiting electrons. Mass number - The total number of protons + neutrons (A), known as nucleons. This is normally written: AX where X is the chemical symbol for that element Z

Example Carbon can be represented by 12C 6 Where no. of protons (atomic no.) = 6 No. of protons and neutrons (mass no.) = 12

Atomic Number & Isotopes Every element has a different atomic number and these are arranged in increasing order in the periodic table. Nuclei which have the same atomic number can have different mass numbers, i.e. same number of protons but different numbers of neutrons, eg: These nuclei (neon in the case above) are known as isotopes. It is also possible for atoms of different elements to have the same mass number.

The relative masses and charges of the proton, neutron and electron are: Particle Mass Charge Symbol Proton 1 + 1 1 p Neutron 1 n electron 1/1840 - 1 0 e -1

Radioactive decay Many nuclei are unstable. In order to achieve stability, they can emit nuclear radiation in the form of alpha, beta or gamma. Such unstable nuclei are called radioisotopes (or radionuclides). This process of emitting radiation is called decay.

Radioactive decay Unstable nuclei are called radioisotopes (or radionuclides) and emit nuclear radiation in the form of alpha, beta or gamma. This process is called Nuclear Decay

Decay Summary Radiation Nature Symbol Alpha particle Helium nucleus 2 Beta particle Fast electron 0 e β -1 Gamma ray High frequency em wave γ

Radioactive decay In alpha decay, the mass number loses 4 and the atomic number loses 2. The resulting isotope (known as the daughter isotope) is a different element. In beta decay, the mass number remains the same and the atomic number gains one. The daughter isotope is a different element. In gamma decay, there is no change in the isotope, only energy is emitted.

Alpha decay Beta decay Radioactive decay of Radium (226) 226Ra → 222Rn + 4He 88 86 2 Beta decay Radioactive decay of Polonium (218) 218Po → 218At + 0e 84 85 -1

2010 Qu: 30 2010 Qu: 30 a, b